The research outlined in this proposal is designed to provide new information concerning the role(s) of vitamin A in insect vision. Tritiated vitamin A will be presented to the yellow fever mosquito, Aedes aegypti L., with the following objectives in mind: (1) the localization of vitamin A to the photoreceptor cells; (2) the determination of the photoreceptor organelles with which vitamin A is associated during different stages of the visual cycle; (3) the quantitative determination of the importance of vitamin A to the functioning of individual photoreceptor cells; (4) the demonstration of the transfer of vitamin A from the adult mosquito to the offspring; and (5) the determinatiin of non-visual tissues and organs involved in the uptake and metabolism of vitamin A. Autoradiography at both the light and the electron microscope level will be used to trace the movement of vitamin A into and through the photoreceptor cells. Liquid scintillation counting, along with autoradiography, will be used to determine whether or not a transfer of vitamin A from adult to offspring does occur. Intracellular recordings of the electrical responses of individual photoreceptor cells to light will be made to determine quantitatively the importance of vitamin A to visual function.